The present invention relates to methine compounds useful as photographic materials, medicines and the like.
In the field of photographic science, the methine compounds of the present invention belong to materials useful as spectral sensitizing dyes like compounds described in, for example, U.S. Pat. Nos. 2,388,963, 2,454,629, 2,927,630, 3,979,213 and 3,796,733, French Patent Nos. 2,117,337 and 1,486,987 and West German Patent No. 2,120,323. In particular, the methine compounds of the present invention belong to so-called rhodacyanine dyes. However, by replacing the methine chain of these compounds with nitrogen atom, the absorption wavelength of them becomes shorter than that of the ordinary rhodacyanines. Therefore, these compounds are effectively useful when a spectral absorption sensitivity at a wavelength shorter than that of ordinary rhodacyanines is necessitated. Although rhodacyanines having a nitrogen atom in place of the methine chain have been already disclosed in, for example, U.S. Pat. No. 2,388,963, the solubility of these compounds is poor, which poses a problem when they are incorporated into a photograhic emulsion.
On the other hand, also in medical and pharmaceutical fields, it has been found that the compounds of the present invention are usable as medicines such as antitumor agents. However, also in these fields, short absorption wavelengths of solutions of them or, in other words, the solutions having a light color are preferred, since they do not make the patients feel uneasy. Also in these fields, the solubility is an important problem. In particular, the methine compounds should not be precipitated or aggregated in a medium having a high salt concentration such as blood in a living body.
Thus the color tone and solubility of the compounds are important points in both fields.